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Martian Glass on Dr. Robert Hargraves’ Crater


Hargraves Crater appears in blue surrounded by impact other impacts in yellow and red and the canyon of Nili fossae

Hargraves Crater appears in blue surrounded by impact other impacts in yellow and red and the canyon of Nili fossae occurs to the left. Blue indicates low topography. Image courtesy of NASA/JPL-Caltech/Arizonia State


On Earth, glass formed at meteorite impact sites has proven to encapsulate and preserve organic molecules and macrostructural life forms much like ancient amber deposits do.  This past summer planetary geologist Prof. Jack Mustard and his graduate student, Kevin Cannon, at Brown University reported in Geology magazine that they had found impact glass in several craters on Mars.  This discovery is particularly relevant to the Martian crater named after the late Princeton geoscience professor, Robert B. Hargraves *59.  Mustard and his colleagues are proposing to land the Mars Rover 2020 on the impact ejecta from Hargraves Crater, which also appears to have a glass-rich spectral signature, as part of their exploration of Nili Fossae (see figure 2).  The Mars Rover 2020 will then select and cache samples containing biosignatures for return to Earth as part of a follow up mission.  

There are other reasons that the impact glass story has caught so much attention.  As professor Tullis Onstott, who teaches a course on astrobiology called “Life in the Universe”, explains, “Glass also serves as an excellent substrate for microbes and they leave behind trace fossils in the form of distinctive etch pits.”  Thus, Onstott has been keeping his eye on the Hargraves Crater developments.  Finding signs of ancient Martian life preserved in a sample of impact glass that originated from Hargraves Crater would not only be an honor for the Geosciences Department, but would be highly appropriate.  In the mid-seventies, Hargraves, then a full professor in the Geology Department at Princeton University, was the principal investigator of the magnetic properties experiment on the Viking missions to Mars.  Viking landers 1 and 2 were the first spacecraft to land successfully on Mars.  To complete surprise of everyone, Hargraves discovered that the Martian dust was extremely magnetic.  His observations defied the conventional wisdom held by many geologists at the time that Martian dust was simply finely comminuted volcanic rock or ash.  Hargraves also spent much of his career studying large impact structures on the Earth.

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